1. Field of the Invention
The present invention relates generally to memory modules. More particularly, the present invention relates to memory module form factors that maximize memory density.
2. Description of Related Art
One aspect of the evolution of computer systems is that operating systems and software have become more memory-intensive. In fact, this particular trend has become so marked that the memory industry has had a very difficult time keeping up with the demand, both from a supply and development standpoint.
Dynamic Random Access Memory (DRAM) semiconductor chips are the primary components used in memory systems. DRAM's are generally made using complimentary metal oxide silicon technology ranging from 0.8 to 0.3 microns in size, with the smaller sizes becoming increasingly prevalent.
While DRAM's have been getting smaller in size, their density has been increasing rapidly. For example, several years ago, 1 Mb and 4 Mb DRAM chips were standard. Today, 16 Mb chips are standard; 64 Mb chips are on the horizon; and 256 Mb and 1 Gb chips are being developed and made.
Also, DRAM packaging has been evolving. Several years ago, memory was pin throughhole packaged. Today, with the common use of surface mount technology, small outline integrated circuit (SOIC), thin small outline package (TSOP), and like configurations are most common.
Memory modules serve at least two functions. One function is to make DRAM's compatible with the system bus organization, that is, reflective of the system designer' desire to match the processor bus size. Second, memory modules allow for easy upgrades.
Today, memory modules come in four basic types: one-byte modules (30-pin single-in-line memory modules (SIMMS), four-byte modules (72-pin SIMMs or 72-pin small outline, dual in-line memory modules (SODIMMs), eight-byte modules (168-pin DIMMs), and custom modules (e.g., HP 9000 workstation memory). SIMMs were first developed by Wang in the mid-1970's in conjunction with Molex, the connector supplier for Wang's "office assistant" word processor. While SIMMs have, generally, 30 or 72 contacts that are the same on both sides of the "card," DIMMs have two (dual) rows of contacts, one row on each side of the card. With the additional pins, a computer can retrieve information from DIMMs 64 bits at a time instead of the 32 or 16-bit transfers usual with SIMMs. SODIMMs have 72-pins, making them relatively compact and thus particularly well suited for memory expansion in portables.
Notwithstanding all of the foregoing developments, there still remains an urgent need to continue to develop methods and apparatus for maximizing DRAM density within the space constraints of existing computer systems. To the extent this has been attempted or effected by manipulating the form of memory modules, system designers have made modules higher or taller. In many systems there is a limit as to how high or tall such a module can be, limiting usefulness of this approach. It is a shortcoming and deficiency of the prior art that heretofore there has not been envisioned a way to maximize DRAM density in systems, by manipulating the form of memory modules in a way that does not make them too tall to fit in many systems.